The present invention relates to a calender having a supporting frame and a set of rolls attached to vertical portions of the supporting frame so as to form a stack of rolls in which adjacent rolls are arranged one above the other forming calendering nips therebetween, the stack including a top roll, a bottom roll and a plurality of intermediate rolls arranged between the top roll and the bottom roll. The invention also relates to a method of rebuilding a calender where the structure of an existing calender is employed in the constructing a modernized calender.
The set of rolls in a calender conventionally comprises a plurality of rolls which are arranged one above the other as a stack of rolls. The rolls are placed one above another and adjacent rolls in the stack are in nip contact with one another, the nips defined between adjacent rolls being structured and arranged for calendering a paper or board web or equivalent run between the nips of the rolls. The rolls are journaled on bearing housings for permitting the rotation of rolls, which in turn are normally attached to slides fitted on vertical guides provided in the frame of the calender. The slides are suspended through spindle nuts on vertical lifting spindles provided in the frame of the calender. Thus, the rolls of the set of rolls are not rigidly fixed at their bearing housings to the frame of the calender, but, instead, the rolls can move in a vertical direction.
The mass of the bearing housings of the rolls and the auxiliary devices attached thereto, such as, fly rolls, are quite large, and as such, cause in conventional calenders the considerable drawback of distortions in the distribution of the linear loads of the nips. For this reason, calenders have started to incorporate relief devices which are supported on the slides of the rolls, on one hand, and on spindle nuts provided on the lifting spindles, on the other hand. In this manner, distortions caused by the weight of the bearing housings of the rolls and the auxiliary devices attached thereto in the linear load profiles between the rolls can be relieved by means of relief devices. One such arrangement is disclosed in U.S. Pat. No. 4,901,637, the entire disclosure of which is incorporated herein by reference.
The use of relief devices is previously known also from conventional machine calenders, in which attempts are made to eliminate, in particular, by means of hydraulic relief cylinders, the above-mentioned effect of concentrated loads arising from the bearing housings of the rolls and from auxiliary devices.
New supercalenders have begun to employ polymer rolls as soft rolls instead of fiber rolls, whereupon the total height variation of the set of rolls has remained considerably smaller than in conventional supercalenders that use fiber rolls. One reason for this reduced total height variation has been the fact that variations in the diameters of soft rolls are very small because the grinding allowances of these rolls are small. This reduced total height variation has enabled the complete omission of lifting spindles and the slides associated with conventional sets of rolls in a supercalender, and it has been possible to replace this construction with a so-called a pivotal set of rolls, where the intermediate rolls of the set of rolls are mounted on the frame of the calender by means of articulated arms pivotally mounted to the frame. This arrangement is possible since variations of the total height of the set of rolls are small, the vertical distance of movement required by an individual roll is small, and because of this, irrespective of the articulated attachment of the rolls, the movements of the rolls relative to the nip level are very small when adjusting the height position of the roll.
Articulated sets of rolls of the type discussed are disclosed, in U.S. Pat. No. 5,438,920, U.S. Pat. No. 5,806,415, and the international application whose publication number is WO 98/50628. The entire disclosures of these three publications are incorporated herein by reference.
The modernization of a calender having spindles to move the rolls in the direction of the stack to a multi-nip calender having pivotal arms for holding the rolls involves a lot of work, because many operations have to be performed on existing constructions, such as the calender frame.
Accordingly, it is an object of the present invention to provide a calender which meets the demands of modem calender constructions and up-to-date multi-nip calenders by using existing calender constructions in a simple manner.
It is another object of the invention to provide a method for rebuilding an existing calender into a modernized multi-nip calender.
With a view to attaining the objects of the invention set forth above, the intermediate rolls are attached to arms pivotable on auxiliary frames, which in turn are attached to vertical portions of the supporting frame of the old calender. With the help of auxiliary frames, all the necessary equipment for modernization can be incorporated in the frame of the old calender, and the vertical portions of the old frame that is, the vertical posts designed to carry the vertical spindles and shaped to act as guides for the bearing housings of the rolls need only be changed in view of the mounting the auxiliary frames.
The auxiliary frames can be designed as profiles which in part clamp around the old guides of the frame, and, being composed of several parts wrap around the existing vertical portions of the old calender frame. The arms supporting the intermediate roll at both ends thereof can each be pivoted to this profile to both lateral portions thereof on opposite sides of the vertical portion of the old frame. The arms can also provide a place for mounting revolvingly the inner fly rolls that have existed inside the old calender frame.